Recording sheet employing an aromatic carboxylic acid

ABSTRACT

1. A RECORDING SHEET COMPRISING A SUPPORT HAVING THEREON A LAYER OF COLOR DEVELOPER CAPABLE OF REACTING WITH A SUBSTANTIALLY COLORLESS COLOR TO FORM A COLORED IMAGE WHERIN SAID COLOR DEVELOPER CONSISTS ESSENTIALLY OF AT LEAST ONE CLAY AND AT LEAST ONE AROMATIC CARBOXYLIC ACID OR AN ALKALI METAL SALT THEREOF.

United States Patent 3,843,383 RECORDING SHEET EMPLOYING AN AROMATICCARBOXYLIC ACID Sadao Ishige, Kanagawa, and Takao Hayashi and HajimeKato, Shizuoka, Japan, assignors to Fuji Photo Film Co., Ltd., MinamiAshigara-shi, Kanagawa, Japan No Drawing. Filed Oct. 30, 1972, Ser. No.301,925 Claims priority, application Japan, Oct. 28, 1971, 46/235,834Int. Cl. B41m 5/00 US. Cl. 11736.8 12 Claims ABSTRACT OF THE DISCLOSUREA recording sheet comprising a support having thereon a layer of colordeveloper capable of reacting with a sub stantially colorless colorformer to form colored image wherein said color developer comprises atleast one clay and at least one aromatic carboxylic acid or an alkalimetal salt thereof.

BACKGROUND OF THE INVENTION Field of the Invention The present inventionrelates to a recording sheet and, more particularly, it relates to theimprovement in the color developer which reacts with a nearly colorlesscolor former to form a developed color image.

Description of the Prior Art In a recording sheet, as is well known fromUS. Pats. 2,712,507; 2,730,456; 2,730,457; 3,418,250, etc.,microcapsules containing a solution of a nearly colorless organiccompound (hereinafter referred to as color former), and a compound whichreacts with said color former to develop color (hereinafter referred toas color developer) are utilized.

A variety of forms of application are known. For example, there is apressure sensitive copying sheet comprising a sheet coated withmicrocapsules containing color former solution (i.e., color former sheetor upper sheet), a sheet coated with a color developer together with abinder (i.e., color developer sheet or lower sheet) and, in some cases,a sheet one side of which is coated with a color developer and the otherside of which is coated with microcapsules (i.e., middle sheet). Asanother embodiment, there is a sheet wherein the microcapsules and thecolor developer are applied to the same surface of a support (i.e.,single recording sheet).

Furthermore, a heat-sensitive recording sheet is also known which hasthe same basic elements as above and is coated with a color former and acolor developer on the same or different supports. In this case, aheat-meltable material such as acetanilide is added to a layercontaining the color former.

As still a further embodiment, a printing process wherein a colordeveloper sheet and a color former ink are combined is also known.

As the above-described color developer, there have generally been usedclays such as acid clay, active clay, attapnlgite, zeolite, hentonite,etc., organic acids such as succinic acid, tannic acid, gallic acid,etc., phenol resins, and the like. Acid clay, of course, is commonlyavailable, through produced in Japan, and has properties similar toattapulgite.

However, the use of such materials is subject to the defect that whensuch color developers are used singly, or even, for example, when claysand a phenol compound are used in combination, the developed colorimages obtained by the reaction with a color former such as CrystalViolet lactone, 3-methyl-2,2'-spirobi(benzo-f-chromene),

3,843,383 Patented Oct. 22, 1974 ice SUMMARY OF THE INVENTION One objectof the invention is to provide an improved recording sheet withoutlosing the advantages of the color developer clays.

Another object of the invention is to improve the light resistance of adeveloped color image formed by a color former and clays.

The above-mentioned objects of the invention are attained byincorporating at least one aromatic carboxylic acid or an alkali metalsalt thereof in a clay used as a color developer.

The term recording sheet as used herein defines a support having thereonat least one color developer layer as described above used for recordingutilizing the coloring reaction between a color former and a colordeveloper. Therefore, all the above-stated embodiments are includedtherein.

DETAILED DESCRIPTION OF THE INVENTION As the clays used in theinvention, there can be illustrated, for example, acidic clay, activeclay, attapulgite, zeolite, bentonite, kaolin, silicic acid, syntheticsilicic acid, aluminum silicate, zinc silicate, etc. Colloidal silicicacid and the like may also be employed as the clays in accordance withthe invention. In general, any of the may clay materials used by theprior art to react with a colorless basis dye to yield a coloredreaction product may be used in the present invention. Clays prepared bychemically processing such clays can also be employed; for instance,those clays which have been subjected to known treatments with a mineralacid or alkaline material to improve certain properties thereof. Suchclays may also be subjected to physical processing, e.g., crushing, toreduce the particle size thereof, if desired.

As the aromatic carboxylic acid used in the present invention there arearomatic compounds having at least one carboxyl group, e.g., benzoicacid, aminobenzoic acid (the 0-, mand p-derivatives can be used),hydroxybenzoic acid the o-, mand p-derivatives can be used),nitrobenzoic acid (the o-, mand p-derivatives can be used),2-hydroxy-3-naphthoic acid, 2-hydroxyl-1-naphthoic acid,4-amino-1-naphthoic acid, 4-nitro-2-hydroxyl-l-naphthoic acid,2,4-dihydroxy-benzoic acid, 2,4,6-trihydroxy-benzoic acid,2-hydroxy-4-aminobenzoic acid, acetaminobenzoic acid (the o-, mandpderivatives can be used), 2-hydroxyA-methylbenzoic acid,2-amino-4-tert-butylbenzoic acid, 2,6-dihydroxy-4-ethylbenzoic acid,2-hydroxy 5-tertbutylbenzoic acid, 3-phenylsalicylic acid,3-methyl-5-tertbutylsalicylic acid, 3,S-di-tert-butylsalicylic acid,3,5-ditert-amylsalicyclic acid, 3-cyclohexylsalicylic acid,5-cyclohexylsalicylic acid, 3-methyl-5-isoamylsalicylic acid, 3,S-di-sec-butylsalicylic acid, 5 sec-butylsalicylic acid, 5-nonylsalicylic acid, 3,S-di-isopropylsalicylic acid, and the like. Ofthese compounds, those having at least one hydroxy group areparticularly effective.

As the alkali metal salts of the organic carboxylic acid, there can beillustrated, for example, sodium, lithium, or potassium salts of theabove-mentioned organic carboxylic acids, and the like.

In the case of these mental salts, aromatic'carboxylic acids having atleast one or more hydroxyl groups are especially effective.

The most preferred organic carboxylic acids or alkali metal saltsthereof used in the present invention have at least one hydroxyl groupand further one or more alkyl groups with 4 to 12 carbon atoms, a phenylgroup and/ or a cyclohexyl group.

The amount of the aromatic carboxylic acid or alkali metal salt thereofis preferably about 1 to about 200 parts by weight, more preferably to60 parts by weight, based on 100 parts by weight of the clay. Whilelesser amounts can be used, insufficient results are often encountered,and at much greater amounts the improvement in results is notsignificantly bettered in most cases to warrant the use of additionalacid.

As the process for producing the color developer in accordance with theinvention, there are, for example, the following processes, but thepresent invention is not limited to the following production examples,since the etfects of the invention naturally occur when at least one ormore clays and at least one or more aromatic carboxylic acids or alkalimetal salts thereof co-exist.

(1) At least one aromatic carboxylic acid or an alkali metal saltthereof is dissolved or dispersed in water and then a clay is dispersedtherein with stirring. Thereafter, the pH of the dispersion is adjustedto a value suitable for the clay used, and a binder such as a latex,polyvinyl alcohol, gum arabic, starch, etc. is added thereto to preparea coating solution. The amount of the binder is usually greater thanabout 5 parts by weight and is preferably to parts by weight per 100parts by weight of the clay.

The resultant coating solution is applied to a support such as a paper,paper substitute, film, etc. in an amount of above about 3 g./m.preferably 4 to 8 g./m. then dried. In this production process, anamount of aromatic carboxylic acid or the salt thereof greater thanabout 0.5 parts by weight, preferably 5 to about 200 parts by weight,per 100 parts by weight of the clay is preferred.

(2) After dispersing the clay in water, the pH of the dispersion isadjusted to a value appropriate for the clay used. Then, a binder isadded thereto. The amount of the binder used is above about 5 parts byweight, preferably 10 to about 30 parts by weight, per 100 parts byweight of the clay.

The coating solution prepared as above is then applied to a paper, resinfilm or paper substitute in an amount of above about 3 g./m. preferably4 to 8 g./m.

Thereafter, an aromatic carboxylic acid or an alkali metal salt of anaromatic carboxylic acid is dissolved or dispersed in water or anorganic solvent such as methanol, ethanol, benzene, acetone, ethylacetate, etc., and, if necessary, in the aqueous system, a binder suchas a latex, polyvinyl alcohol, maleic anhydride-styrene copolymer, etc.,preferably which dissolves in the aqueous system, is added, or, in theorganic solvent system, a binder such as ethyl cellulose,styrene-butadiene copolymer, etc. is added thereto.

The resulting coating solution is then applied to the previously coatedclay to obtain a co-existing system of clay and an aromatic carboxylicacid or the alkali metal salt thereof. In this case, the amount of thebinder used is suitably less than about 10 parts by weight per 100 partsby weight of the aromatic carboxylic acid or alkali metal salt thereofand the amount of the coating solution is suitably above about 0.1 g./m.desirably 0.3 to 1.0 g./m. The upper limit of the amount coated isdecided primarily by economic considerations.

The dispersion pH adjustment referred to above is accomplished by addingan alkaline material to the dispersion to render the pH thereofalkaline. This preferred step increases the color developing ability ofthe system, with best results usually being provided at a pH of fromabout 8 to about 10.5. Any alkaline material compatible with recordingsheet systems can be used, but normally an 4 alkali hydroxide is usedbecause of the high solubility of such compounds.

In the above-described case where an organic solvent is used, the effectof the invention becomes larger when a solvent capable of dissolving thearomatic carboxylic acid or the alkali metal salt is used. :In suchcases, binders are rarely required, though if used they preferably aredissolved in the organic solvent.

There is no limit on the binder which may be used in the presentinvention, that is, the binder used in the present invention can beselected from any of those as are used in the prior art, and the exactbinder used is not overly critical. Examples of binders in addition tothose listed above which can be used are gelatin, casein, sodiumalginate, carboxymethylcellulose, a latex of a material such aspolyvinylacetate, styrene-butadiene copolymers, styrene-acrylic acidcopolymers, butadiene-acrylic acid copolymers or polyacrylates.

The layer containing the color developer of the invention may furthercontain acidic resins such as a phenolformaldehyde resin, or inorganicpigments such as metal oxides, metal hydroxides, etc.

Preferred phenol resins are described in U.S. Pats. 3,516,845;3,427,180; and 3,455,721, for example, a pphenylphenol-formaldehydecondensate, a p-tert-butylphenol-formaldehyde condensate or aphenol-acetylene condensate.

Preferred inorganic pigments include metal oxides such as Zinc oxide,magnesium oxide or titanium oxide, metal hydroxides such as calciumhydroxide, magnesium hydroxide or zinc hydroxide, and metal carbonatessuch as magnesium carbonate, zinc carbonate and calcium carbonate.

In addition, each coating solution may be applied to either the wholesurface or may be only partly coated (printed) on the surface.

The coating solution prepared in the above examples may be coated on asupport together with the color formers described hereinafter. When usedas a pressure sensitive paper, the color former may be contained inmicrocapsules.

The color former is usually dissolved in a solvent well known in theart, such as chlorinated diphenyl, chlorinated parafiin, benzene,toluene, etc., and encapsulated in microcapsules, or is dissolved in theabove-described solvent and, after adding a binder thereto, applied to asupport. In the latter case, the solution may be supplied to a colordeveloper sheet through a stencil or like pattern in ink-like forminstead of coating onto the support. In the case of a heat-sensitivecopying paper, known heat-meltable materials such as acetanilide, urea,alphaor beta-naphthol, phthalic anhydride, stearic acid, etc. are mixedwith the color former and applied to a support. Preferably the ratio ofthermofusible substance to the color former is 1.5 to 30 wt. percent.

As described above, with respect to the color former, the solventtherefor, the additives thereto, encapsulating methods, etc., any ofthose known in the art can be suitably selected and employed.

However, the kind of color former used is not critical in thisinvention. Examples of the color former usable in this invention aretriarylmethane compounds such as 3,3 bis(p dimethylaminophenyl) 6dimethylamino phthalide, i.e., Crystal Violet Lactone 3,3-bis(pdimethyl-aminophenyl) phthalide, i.e., malachite green lactone, 3 (pdimethylaminophenyl) 3 (1,2-dimethylllldOl 3 yl)phthalide, 3 (pdimethylaminophenyl)- 3-(2 methylindol 3 yl)phthalide,3-(p-dimethylaminophenyl) 3 (2-phenylindol-3-yl)phthalide, 3,3-bis(1,2,- dimethylindol 3 yl)-5-dimethylaminophthalide, 3,3- bis(1,2-dimethylindol 3 yl)-6-dimethylatninophthalide, 3,3bis(9-ethylcarbazol-3-yl) 5 dimethylaminophthallcle, 3,3-bis(2phenylindol 3 yl)-5-din1ethylaminophthalide, and 3 pdimethylaminophenyl-3-(l-methylpyrrol 2 yl) 6 dimethylamino-phthalide;diphenyl methane compounds such as 4,4'-bis-dimethyl aminobenzhydrinebenzyl ether, N-halophenyl-leuco Auramine and N-2,4,5-trichl0rophenylleuco Auramine; xanthene compounds such as rhodamine-B anilinolactam,rhodamine (p-nitroanilino)lactam, rhodamine B (p-chloroanilino)lactam, 7dimethylamino 2 methoxyfluoran, 7-diethylamino 2 methoxyfluoran, 7diethylamino-3- methyoxyfluoran, 7 diethylamino 3 chlorofluoran,7-diethylamino 3 chloro 2 methylfluoran, 7-diethylamino-2,3dimethylfluoran, 7-diethylamino (3-acetylmethylamino)fiuoran,7-diethylamino (3 methylamino)fluoran, 3,7 diethylaminofluoran, 7diethylamino-3- (dibenzyl-amino)fluoran, 7 diethylamino 3(methylbenzylamino)fiuoran, 7-diethylamino 3(chloroethylmethylamino)fluoran and 7-diethylamino 3(diethylamino)fluoran; thiazine compounds such as benozyl leucomethyleneblue and p-nitrobenzyl leucomethylene blue; and spiropyran compoundssuch as 3-methyl-spiro dinaphthopyran 3 ethyl-spiro-dinaphthopyran,3,3-dichloro-spiro-dinaphthopyran, 3-benzyl-spiro dinaphthopyran,3-methyl naphtho (3-methoxybenzo)spiropyran and3-propyl-spiro-dibenzopyran.

In general, a combination of crystal violet lactone which has a rapidcolor-forming property when contacted with clay, and benzoylleucomethylene blue which has a slow color-forming property but which iscapable of forming a color of greater light-resistance is preferablyused.

However, when a sheet having thereon microcapsules containing the colorformer of the above described combination is contacted, for example,under pressure, with a conventional clay-coated paper or a colordeveloper sheet wherein a phenol resin is used, a long time is requiredbefore benzoyl leucomethlene blue forms a color after the momentarycolor formation of the Crystal Violet lactone, and, in addition, thedeveloped color image of Crystal Violet lactone becomes faint.

In a color developing sheet utilizing a phenol resin, this tendency isparticularly great, because benzoyl leucomethylene blue scarcely formsany color.

When the color developer in accordance with the invention is used, theabove-described defect is completely removed.

In short, the recording sheet of the invention is characterized by acolor developer wherein clays and at least one aromatic carboxylic acidor an alkali metal salt thereof is used, and, as a result, variouscapabilities required for a color developer, such as light resistance ofthe developed color image and the like are remarkably improved.

(1) Light resistance of the developed color image The developed colorimage formed by using the color developer of this invention does notfade as much when it is irradiated with sun-light or left in a room, ascompared to a conventional clay-coated paper. This markedly contributesto the market value of the product.

(2) Color-developin g ability The color-developing ability of the colordeveloper in accordance with the present invention is so improved, ascompared with a conventional clay-coated paper, that either the amountof the color developer on a support or the amount of the color former ona color former sheet can be reduced to obtain the same color density.

In particular, the reduction in the amount of the color former usedresults in reducing the cost of producing recording sheets.

(3) Activity with the passage of time The activity of a conventionalclay-coated paper is reduced with the passage of time due to theadsorption of ambient materials, whereas with the color developer ofthis invention a reduction in the color-developing ability with thepassage of time is hardly observed.

It will now be shown by the following Examples of the color developer ofthe invention, i.e., the color developer wherein at least one aromaticcarboxylic acid and/ or an alkali metal salt thereof is incorporated ina clay, has a markedly improved market value as compared with aconventional color developer clay. The present invention, of course, isnot to be limited only to such Examples, however.

The effect of the recording sheet of the invention was confirmed usingthe following color former.

The microcapsules containing the color former were prepared according tothe description of, for example, US. Pat. 2,800,457 Green et al. Aspecific example thereof is shown below. Hereafter, parts are all byweight unless otherwise indicated.

10 Parts of acid-processed pigskin gelatin and 10 parts of gum arabicwere dissolved in 400 parts of 40 C. water, and 0.2 parts of Turkey redoil was added thereto as an emulsifying agent. 40 parts of colorformer-containing oil was emulsified in the resulting solution, thecolor former-containing oil being prepared by dissolving 2% of CrystalViolet lactone in a mixed oil comprising 4 parts of chlorinated diphenyland 1 part of lamp oil.

When the size of the oil droplets became 5 microns on the average,emulsification was discontinued, 40 C. water was added thereto to makethe total 900 parts, and stirring was continued. Thereafter, the pH ofthe solution was adjusted to 4.0 to 4.2 by the addition of 10% aqueousacetic acid to cause coacervation.

After stirring for a further 20 minutes, the solution was cooled withice Water to cause gelation of the coacervate membrane deposited aroundthe oil droplets.

When the temperature of the solution became 20 C., 7 parts of 37%formalin was added thereto. At 10 C., the pH of the solution wasadjusted to 9 by the addition of a 15% aqueous sodium hydroxidesolution. The addition of sodium hydroxide was conducted slowly.Subsequently, the temperature of the solution was raised to 50 C. over a20 minute period while stirring.

After adjusting the temperature of the microcapsule dispersion thusobtained to 30 C., the dispersion was applied to a 40 g./cm. paper incoated amount of 6 g./m. (solid components) and then dried.

In the manner as described above, there was obtained a sheet havingthereon microcapsules containing as the color former Crystal Violetlactone.

Microcapsule-coated sheets containing other color formers were alsoprepared in the same manner as above merely by changing the identity ofthe color former.

The following developer materials were then formed. The particle size ofthe clay materials used in the examples was 5 microns.

EXAMPLE 1 8 Parts of a 20% aqueous sodium hydroxide solution was addedto 300 parts of water, and 10 parts of the following aromatic carboxylicacid was dissolved or dispersed therein. Thereafter, parts of acid claywas gradually added thereto with stirring. 20 g. (solid components) ofstyrene-butadiene latex (SBR latex) was added thereto, and the pH of thedispersion was adjusted to 9.5 by the addition of a 20% aqueous sodiumhydroxide solution.

The coating solution so obtained was applied onto a 40 g./m. base paperto provide a 5 g./m. solid component coating thereon by means of acoating rod, then dried. There was thus obtained a color developer sheetin accordance with the invention.

EXAMPLE 2 100 Parts of acid clay was dispersed in 300 parts of waterwith stirring. Subsequently, 15 parts of the following aroma-ticcarboxylic acid or the alkali metal salt thereof was added thereto.Then, a 20% aqueous sodium hydroxide solution was gradually addedthereto and, at a pH of 8, 20 parts (solid components) of SBR latex wasadded thereto and the pH of the solution was adjusted to 9.5 with theaqueous sodium hydroxide solution. The coating solution thus obtainedwas applied to a 40 g./n1. base paper to provide a g./m. solid componentcoating thereon by means of a coating rod, then dried. There was thusobtained a color developer sheet in accordance with the inventionEXAMPLE 3 After dispersing 100 parts of finely pulverized silicic acidin 300 parts of water, parts of the following aromatic carboxylic acidor the alkali metal salt thereof was added thereto, and subsequently,100 parts of a aqueous polyvinyl alcohol solution was added thereto.Thereafter, the pH of the dispersion was adjusted to 6.0 with a 20%aqueous sodium hydroxide solution. The coating solution thus obtainedwas applied to a 40 g./m. base paper to provide 4 g./m. solid componentscoating by means of a coating rod, then dried. There was thus obtained acolor developer sheet in accordance with the present invention.

EXAMPLE 4 100 parts of acid clay was dispersed in 300 g. of water withstirring. Subsequently, 5 parts of the following aromatic carboxylicacid and 5 parts of the following alkali metal salt of the aromaticcarboxylic acid were added thereto. Then, a 10% aqueous sodium hydroxidesolution was gradually added thereto and, at a pH of 8, 20 parts (solidcomponents) of SBR latex was added thereto. Further, the pH of thesolution was adjusted to 9.5 with a 10% aqueous sodium hydroxidesolution. The coating solution thus obtained was applied to a 40 g./m.base paper to give a 5 g./m. solid component coating by means of acoating rod. There was obtained a color developer sheet in accordancewith the present invention.

EXAMPLE 5 8 Parts of a 20% aqueous sodium hydroxide solution was addedto 300 parts of water, and 100 parts of acid clay was graduallydispersed therein with stirring. Thereafter, 20 parts (solid component)of a SBR latex was added thereto to prepare a coating solution. The pHof the coating solution was 9.5.

The resulting coating solution was applied to a 40 g./m. base paper togive a 5 g./m. solid component coating thereon by means of a coatingrod, then dried.

Thereafter, 50 parts of the following aromatic carboxwas thus obtained acolor developer sheet in accordance with the invention.

Comparative Example 1 100 Parts of acid clay was dispersed in 300 partsof water with stirring, and 8 parts of a 20% aqueous sodium hydroxidesolution was added and then 20 parts (solid component) of SBR latex wasadded thereto to prepare a coating solution. The pH of the resultingcoating solution was 9.5.

This coating solution was applied to a 40 g./ m base paper so that 6g./m. of solid components were coated thereon by means of a coating rod.

Comparative Example 2 100 Parts of finely pulverized silicic acid wasdissolved in 30 parts of water, 100 parts of a 20% aqueous polyvinylalcohol solution was added thereto, and the pH of the dispersion wasadjusted to 6.0 with a 20% aqueous sodium hydroxide solution. Theresulting coating solution was then applied to a 40 g./m. base paper sothat 4 g./m. of solid components were coated thereon by means of acoating rod, then dried.

Comparative Test and the Results Obtained A microcapsule-coated sheetcontaining Crystal Violet lactone or 2,4-dimethyl-7-diethylaminofiuoranprepared as heretofore described was superposed on each of the colordeveloper sheets prepared in Examples 1-5 and Comparative Examples 1 and2, and color was developed by applying a load of 600 kg/cm. thereto.

After leaving the developed sheets for one day and one night in thedark, the reflection absorption spectrum between 380-700 111 1. inwavelength was measured by means of a DB-type Beckman spectrophotometer,and the absorbance (hereinafter referred to as density) at theabsorption maximum was regarded as the fresh or initial density.Furthermore, the color-developed bodies were exposed to sun-light forone hour, and the reflection absorption spectrum at the color-developedsurface was measured to determine the density.

From the data thus obtained, the light resistance value defined by thefollowing formula was determined:

Light resistance value (percent) ylic acid or the alkali metal saltthereof was dissolved The density f the color developed body after ordispersed 1n 300 parts of ethanol 1n which 5 parts of ex Osure to sum htth 1 cellulose had previously been dissolved The resultp g X100 y Freshdensity of the color-developed body mg coating solution was applied tothe above-described acidic lay coated paper in an amount of 0.5 g./m.(solid The fresh density and the light res1stance values thus component)by means of a coating rod, then drled. There determined are given 1nTable 1.

TABLE 1 2,4-dimethyl-7- Crystal violet lactone diethylaminofiuoranExample or Light Light comparative Aromatic carboxylic acid or the Freshresistance, Fresh resistance, example alkali metal salt thereof densitypercent density percent Number:

1 Example 1 1. 01 77. 2 0. 83 99. 3 Comparative 0. 00 59. 8 0. 79 84. 7

Example 1. Example 1 3,5-di-tert-butylsalicylic acid 1.02 76. 4 0.80 96.2 do m-Nitrobenzoic acid 0.99 63.5 0.82 87.3 P-Aminobcuzoic acid. 0. 9871.5 0.78 89.5 P-Anisic acid 0. 99 60. 2 0. 79 88. 82,4-di-hydroxybenzoic acid--. 1.03 78. 3 0. 84 91. 2 2-naphthoic acid 1.00 72. 3 0. 79 96. 0 1.02 76.5 0.81 97.1 y 1. 04 77. 5 O. 82 98. 6S-tert-butylsalicylic acid sodium salt 1.02 74. 3 0.80 97. 8 Potassium2-hydroxy-3-naphthoate. 1. 00 72. 6 0. 81 92. 3 m-Hydroxybenzoic acid1.01 73.6 0.79 91.5 Salicylic acid 1. 03 74.3 0.82 90. 5 Comparative 1.00 48. 9 0. 81 72. 1

Example 2. 14 Example 4 Salicylic acid and sodium 5-tert-butyl- 1.0273.1 0.80 91.2

salicylate. 3,5-di-tert-butylsalicylic acid and potassium 1.05 74. 20.82 93. 6

rn-hydroxybenzoate. Sodium 5-sce-butylsalicylate 1.01 48. 4 0. 83 85. 9Salicylic acid 1.02 76. 9 0.82 98. 2 1. 00 75. 0 0. 81 97. 9

From the results of the data in Table 1, it is seen that the lightresistance of a color-developed body can markedly be improved by the useof a clay and at least one arom-atic carboxylic acid or an alkali metalsalt thereof.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be aparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:

1. A recording sheet comprising a support having thereon a layer ofcolor developer capable of reacting with a substantially colorless colorto form a colored image wherein said color developer consistsessentially of at least one clay and at least one aromatic carboxylicacid or an alkali metal salt thereof.

2. The recording sheet of claim 1 wherein the color developer is anacidic clay.

3. The recording sheet of claim 1 wherein the color former is a basicdye.

4. The recording sheet of claim 1 wherein from about 1 to about 200parts by weight of said aromatic carboxylic acid or alkali metal saltthereof is present per 100 parts by weight of said clay.

5. The recording sheet of claim 1 wherein the arcmatic carobxylic acidor alkali metal salt thereof is substituted with at least one hydroxylgroup.

6. The recording sheet of claim 5 wherein the aromatic oarboxylic acidor alkali metal salt thereof is also substituted with one or more alkylgroups having 4 to 12 carbon atoms, a phenyl group or a cyclohexylgroup.

7. The recording sheet of claim 1 wherein the constituents are carriedin a binder.

8. The recording sheet of claim 7 wherein about 5 to 30 parts by weightof binder are present based on 100 parts by weight of clay.

9. The recording sheet of claim 1 wherein from 5 to parts by weight ofsaid aromatic carboxylic acid or alkali metal salt thereof is presentper parts by weight of said clay.

10. The recording sheet of claim 1 being pressuresensitive copy sheet.

11. The recording sheet of claim 7 wherein up to about 30 parts byweight of binder are present based on 100 parts by Weight of clay.

12. In a process for developing a color image on a recording sheet bythe reaction between a clay and a colorless color former, theimprovement which comprises carrying out said reaction in the presenceof an aromatic carboxylic acid or alkali metal salt thereof.

References Cited UNITED STATES PATENTS 3,746,563 7/1973 Farber et al11736.2 3,664,858 5/1972 Huffman 11736.8 3,689,302 9/1972 Kubo et al11736.8 3,418,250 12/1968 Vassiliades 11736.2 X 3,427,180 2/1969Phillips 1l7-36.8 X

THOMAS J. HER'BERT, JR., Primary Examiner US. Cl. X.R. 252316

1. A RECORDING SHEET COMPRISING A SUPPORT HAVING THEREON A LAYER OFCOLOR DEVELOPER CAPABLE OF REACTING WITH A SUBSTANTIALLY COLORLESS COLORTO FORM A COLORED IMAGE WHERIN SAID COLOR DEVELOPER CONSISTS ESSENTIALLYOF AT LEAST ONE CLAY AND AT LEAST ONE AROMATIC CARBOXYLIC ACID OR ANALKALI METAL SALT THEREOF.